In oil-producing fields employing waterflooding, the water tends to channel through zones of high permeability and tends to by-pass a large amount of oil-in-place. Since waterflooding fluids usually contain chemicals, and even small amounts of chemicals in the hundreds of millions of gallons of water employed becomes expensive, an efficient sweep of the waterflood is important. If high permeability water channels can be blocked, the water is diverted into tighter oil-bearing zones.
Water channeling can be reduced by injecting a solution of a polymer with a polyvalent metal crosslinking agent under conditions which gel the polymer, plugging off the more permeable formation, and diverting the subsequently injected floodwater into the formerly less permeable but now relatively more permeable oil bearing zones. The use of aluminum citrate and related polyvalent metal cations as crosslinking agents has been known for some time. However, the citrate-sequestered aluminum type of agents has not been entirely satisfactory in some of the more hostile environments, such as formation temperatures of greater than about 170.degree. F. and/or hardness cation values in the formation water of greater than about 500 ppm.
Chromium(III) propionate solution is an effective agent for crosslinking such as the partially hydrolyzed acrylamide-based polymers to form a gel in high permeability zones of an oil bearing reservoir, in either near well treatments or indepth applications. Not only is a chromium(III) propionate solution effective for such permeability correction processes, and useful in hard brines, but surprisingly the propionate component is biocidal against the pestiferous sulfate-reducing bacteria usually present in the formation water. Thus, both the crosslinking benefits can be obtained plus the biocidal benefits.
However, the chromium(III) propionate solution must be discretely prepared. Redox methods resulting in sulfate in the product are undesirable because of potential formation damage caused by precipitation of BaSO.sub.4 and/or CaSO.sub.4, and since sulfate can be metabolized by sulfate-reducing bacteria to produce corrosive "souring" gas H.sub.2 S.
Solutions of chromium(III) propionate of good clarity easily and readily prepared in a reproducible manner have been a goal, or perhaps an obstacle, in the path of the use of this highly important material in oil field processes.